1. Field
Provided is a fluorescence detection optical system and a multi-channel fluorescence detection apparatus including the same, and more particularly, a fluorescence detection optical system for detecting fluorescence beams with two or more different wavelengths, and for maintaining a constant focal point through an automatic focusing function, and a multi-channel fluorescence detection apparatus including the fluorescence detection optical system.
2. Description of the Related Art
In accordance with the advent of point of care diagnosis, various medical experiments such as gene analysis, external diagnosis, and nucleic acid sequence analysis, for example, have become important, and demand therefor has been increasing. Accordingly, platforms and systems for expediting a substantially large amount of experiments using a substantially small amount of samples have been developed and released. To meet such demand, microfluidic device platforms, such as a microfluidic chip or a lab-on-a-chip (“LOC”), are receiving attention. Microfluidic devices include a plurality of microfluids and microchambers that are designed to control and manipulate a substantially small amount of fluids. Microfluidic devices substantially minimize a reaction time of microfluids. Simultaneously, microfluidic devices react microfluids, and measure reaction results. Microfluidic devices may be manufactured using various methods, and may be formed of various materials according to manufacturing methods.
During gene analysis, for example, to accurately determine whether a sample includes a specific biological material, such as deoxyribonucleic acid (“DNA”), or an amount of the specific DNA, a process of refining/extracting a real biological sample and sufficiently amplifying the refined/extracted sample is needed. Polymerase chain reaction (“PCR”) is most widely used among various methods of amplifying a gene. A fluorescence detection method is mainly used to detect DNA amplified through PCR. For example, quantitative real-time PCR (“qPCR”) uses a plurality of fluorescent dyes/probes and primer sets to amplify a target biological sample and detect/measure the amplified target sample in real time. For example, qPCR uses a fluorescence characteristic by cutting a TaqMan® probe from a template during DNA amplification. More specifically, as a PCR cycle develops, a number of TaqMan® probes cut from templates exponentially increases, and thus a fluorescence signal level exponentially increases. Such an increase in the fluorescence signal level is measured using an optical system, which enables determination of whether the target sample includes certain DNA or enables performance of quantitative analysis. As the PCR cycle develops, the fluorescence signal level forms an S-curve. A threshold cycle (“Ct”) value is set at a point where the fluorescence signal level rapidly changes and the fluorescence signal level is measured thereat. Platforms to which qPCR is applied have been commercially used in various experimental analyses such as external diagnosis, gene analysis, development of a biomarker, and nucleic acid sequence analysis.
A fluorescence detection optical system measures a fluorescence signal level or a change of the fluorescence signal level according to a bio reaction that occurs in a microfluidic device such as a microfluidic chip or a PCR chip. When the fluorescence detection optical system is designed and manufactured, it needs to be considered that a depth of a microchamber of the microfluidic device is merely between several micrometers (μm) and several millimeters (mm). Accordingly, a shape of the microchamber is close to that of a two-dimensional (“2D”) chamber since the microchamber has a substantially small depth compared to its width and its length. This means that a range of a focal depth at which a focal point is formed in the microchamber is quite narrow. In particular, when a numerical aperture (“NA”) of an objective lens of the fluorescence detection optical system is increased in order to accurately detect fluorescence, the focal depth is further reduced, for example, to several micrometers (μm). Thus, there is a need for precise position-control and precise horizontal-control on the level of several micrometer (μm) between a fluorescence detection optical system and a microfluidic device. If such controls are not precise, focal points formed between chambers in the microfluidic device are formed differently, and thus it is difficult to uniformly and accurately detect fluorescence. Also, if the microfluidic device is attached to or detached from the fluorescence detection optical system, the fluorescence detection optical system needs to maintain its accuracy, and thus a mechanism for attaching or detaching the microfluidic device needs to be precise and thus is complicated, which increases a volume and manufacturing cost of the fluorescence detection optical system.